In my fictional future universe that provides the background for my novels, I have an early 22nd century event that is referred to simply as “The Flare”. The sun emits a mighty burp, and emits a coronal mass ejection classified as X44, roughly one half the strength of which the sun is capable. This hits planet Earth squarely.

The northern lights are not only visible at the equator, but visible in daylight above 80 degrees north. This direct hit destroys vast amounts of the electronics, and immediately kills or incapacitate roughly ten million people, those unlucky to be using cybernetic implants at the time. The ensuing chaos and damage result in the Vast Depression, which lasts nearly a century. Combined with global warming and other misfortunes, by the 24th century only a billion people are alive, and they tell one another lurid tales of kitchen appliances going mad and killing their masters during the flare. On a more rational level, cybernetic technology is non-existent, and while computers still exist, society isn’t as reliant on them as before the Flare.
Not only is this something that can happen; it’s something that will happen. We had such a solar storm hit Earth in 1859, called the Carrington Event after Richard Christopher Carrington, one of two astronomers at the time to observe it. The entire telegraph system went down, and wires and batteries shorted, causing numerous fires. That storm was estimated at X42, about one quarter the size of the X44 monster from my story.

An X20 would be enough to wipe out half the world’s electrical system and most of the computers. The sun has had X20 bursts in 1972, 1989, 2000, 2003, 2006, and 2011. Fortunately, none of them hit Earth squarely.

It’s only a matter of time.

For now, we’re about as safe as we can hope for: we’re approaching a minimum on the 11 year solar cycle, during which big CMEs are less likely—not impossible, just less likely. And there is speculation that the sun is going into a “Maunder Minimum”, an extended period of solar peace that might last for the better part of a century. The last such was from 1645 to 1715. Some of the Climate denialists have been celebrating this, pretending that the half-a-degree centigrade drop in global irradiation will somehow obviate the greenhouse gas-propelled rise of 3-5 degrees presently forecast. Well, that’s why they are called denialists. But even with the twin minimums, the possibility remains. You’re ‘safer’ in much the same way that you are less likely to die in an auto accident at 60 miles an hour than you are in one at 90 miles an hour.
I know a fellow who is a watchdog for public safety, primarily fire (always a major concern here in the west), but also other natural and man-made disasters that might befall us, and he’s recently been trying to get some sort of government response plan set up for a possible electromagnetic pulse (EMP). He’s worried about the sun, of course, since CMEs can produce EMPs world-wide and do several trillion dollars in just a few seconds. It put the lights out over wide areas for hours in 1978 and 1989, and those were near misses by (relatively) moderate CMEs.

There’s a second thing that can put the lights out, and that’s human agency. Nuclear weapons can create EMPs, but only a millionth of what the sun can produce. The effects would be somewhat limited, and if you were the target of such a device, you probably wouldn’t have much time to enjoy the EMP before the hydrogen bomb exploding over your head resulted in an RUD, or Rapid Unscheduled Disassembly, of your body.

However, there is malign human agency that can put the lights out, for months or even years. I even mentioned it in a piece I wrote a few weeks ago during a period of higher-than-usual political tension: “If in the next few days, we have an electronic meltdown in which the Internet, power grid, and banking system all shut down, then it’s safe to assume that Vladimir Putin just declared—and probably won—World War III against the United States.”

It’s rumored that several nuclear powers have nuclear weapons that can be set off in low Earth orbit, and while there would be no blast damage, the EMP could affect electronics over several hundred square kilometers. To that end, the Pentagon has “hardened” most of their communications, protecting them against such, and, it’s claimed, the Russians have war planes that actually use vacuum tubes, which are resistant to the damage an EMP can cause electronics.

Of far greater consequence is the possiblity that malign entities can hack and shut down computer systems, driving the electrical grid, banking records, nearly all communications and systems controlling dams, sewer system, traffic and hundreds of other vital infrastructure systems into an electronic brick wall, possibly destroying them.

It’s possible that World War Three won’t announce itself with bright blue nuclear flashes, or sudden outbreaks of smallpox in major cities, or horrific gases causing thousands to drop, convulsing, in the streets. No, it may be something as simple as a power black out. We often experience those, of course, and don’t think much of them unless they last more than an hour or so.

If you run into a buddy who lives “off the grid”--solar panels, Tesla batteries, satellite for his TV and computer, and he’s complaining his Internet is gone along with TV, then you might assume war has broken out.

In my story, the real damage comes in the months following the flare, when humanity is suddenly trying to feed and water itself with 19th century technology, only there’s five times as many people as that technology could support. And the money’s no good, because it was vaporized along with the computer systems. Only a few million die during the Flare; and virturally none who weren’t wearing electronic implants. But billions die in the six months following, in the chaos and shortages caused by the sudden collapse of our electronic systems.

That public safety fellow is right to be worried about EMPs and their close cousins, cyberattacks. Both can do untold damage, and may announce themselves with nothing more dramatic than your stereo suddenly stopping and your car engine dying.

There’s not a lot you can do to prevent either, but if you want to have something after the events, learn how to build a Faraday cage. They’re pretty simple, really. And consider getting off the grid as best as you can. If you are in a major city, get out. Take survivalist train, cache supplies somewhere you can get to without cars or other transportation. And best of luck.